| As a new type of aircraft that can achieve global long-distance rapid arrival and flexible maneuverability,hypersonic gliding vehicle has become a hot spot in the military competition of major powers.During the design process of long-range hypersonic glider,how to obtain the high lift-drag ratio at the hypersonic flight speed is the first problem to be solved.At present,the waverider has become an important candidate aerodynamic configuration in the field of long-range maneuvering hypersonic glider design.For the waverider,the leading edge can limit the shock wave and high-pressure gas to its lower surface at high-speed,and has a higher lift-to-drag ratio than the traditional hypersonic configuration.However,due to the complexity of its own configuration,flight environment,and task,a series of problems still exist in engineering applications of hypersonic wave rider,which need further research.This paper takes the waverider hypersonic gliding aircraft as the typical engineering application background,and focuses on the basic problems and key issues such as aerodynamic layout design,high-temperature real gas effect,lateral-directional coupled dynamic stability,and hypersonic unsteady aerodynamic modeling in-depth research and discussion.1.Based on the cone-derived waverider generation method,under the constraints of volume efficiency and lift-to-drag ratio,a high lift-to-drag ratio waverider configuration is designed and generated by viscous optimization.Subsequently,it is modified with thermal protection and static stability being the design objective.Wind tunnel experiments and numerical calculations show that the optimized waverider not only maintains excellent"wave-riding"characteristics and high lift-to-drag ratio,but also has static stability in the longitudinal and lateral directions.The waverider-based hypersonic glider has good aerodynamic performance and has established an object for subsequent research.2.For the problem of high-temperature real gas effect when the aircraft is flying at high altitude and high Mach number,a chemical non-equilibrium calculation module is added on the basis of the existing N-S equation solving program,and the flow around the waverider vehicle under high temperature real gas is simulated.Compared with the numerical results of the calorically perfect gas,the effect of the high-temperature real gas on the aerodynamic force and the heat flow distribution on the surface of the waverider are analyzed and studied.The results show that:1)The high temperature real gas effect will have a significant impact on the structure of the flow field around the waverider and the aerodynamic thermal environment.The heat flow at the stagnation point and its nearby small area of the waverider is significant decreased.2)The high-temperature real gas effect will make the axial-force coefficient of the waverider to increase,the normal-force coefficient and the pitching-moment coefficient to decrease,and the pressure center to move backward.However,the effect of the high-temperture real gas on aerodynamic characteristics is very small in the scope of this paper(H=50km,M_∞=10～20).On the basis of numerical calculations,a high-enthalpy shock wave heat measurement experiment is carried out on the waverider,and the surface heat flow distribution characteristics of the waverider under different angles of attack and sideslip are studied experimentally.The results show that:1)The change of the angle of attack have little impact on the heat flow on the front edge of the waverider,but it will significantly increase the heat flow on the lower surface of the aircraft.2)The change of the sideslip angle will lead to significant increase of the heat flow on the windward side of the leading edge.3.Based on the unsteady N-S equation and proper orthogonal decomposition technique,a time-discrete expression about the POD modal coefficient and the velocity of the rigid body motion of the aircraft is obtained through mathematical derivation.On this basis,combined with the system identification method,this paper proposes an unsteady aerodynamic hybrid reduced-order modeling method.The general structure and characteristics of the nonlinear mixed reduced-order model POD-NARMAX are given.Subsequently,under the assumption of small disturbances,a linear mixed reduced-order model POD-ARX was constructed and numerically verified by 2D and 3D examples.The results show that the POD-ARX model constructed in this paper not only has high calculation accuracy and efficiency in the prediction of unsteady aerodynamic forces,but also shows good broadband characteristics and flow field display capabilities.4.Lateral-directional coupled dynamic stability is a critical problem remaining to be solved for hypersonic waveriders.First,the stability is analyzed based on the eigenvalues of the small-disturbance equations.It’s found that possibilities of lateral-directional coupled dynamic instability exist for the waverider when it’s stable both statically and dynamically for each single degree of freedom.This phenomenon is mainly attributed to its non-axisymmetric,flat,and slender geometric features.Then,to assess the dynamic characteristics of the waverider,the POD-ARX model is coupled with the rigid body dynamics equations,constructing a simulation model for the coupled motion of multiple DOFs—ROM/RBD.Numerical examples show that compared to CFD/RBD,the ROM/RBD model can not only have the similar accuracy,but also improve the efficiency by almost 2 orders of magnitude.Furthermore,the ROM/RBD model is employed to evaluate the lateral-directional dynamic characteristics of the waverider in detail.The phenomenon of lateral-directional dynamic instability is further observed and verified by the ROM/RBD model.Finally,a hypersonic wind-tunnel free flight experiment for the waverider is designed and operated.It’s found that the lateral-directional coupled instable motion does occur in the experiment,which is consistent with the results predicted by the ROM/RBD model.What’s more,the analysis of the motion frequency further demonstrates that the ROM/RBD model is applicable in the prediction of multi-DOFs coupled dynamic stability for hypersonic waverider vehicles. |
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